From the viewpoint of reducing the emission amount of greenhouse gas such as CO2 or the like from a vehicle, there has been disclosed a technical approach to search a route with consideration on environment. According to the approach, for example, if the deviation between a measured value of the emission amount of the greenhouse gas of the vehicle accumulated from a departure position to the present position and an estimated value thereof is equal to or greater than a threshold value, the route is re-searched (refer to Japanese Patent No. 4169650).